This application claims the priority of Japanese patent document 10-106448, filed Apr. 16, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a permanent magnet type dynamoelectric machine in which a plurality of permanent magnets are buried or embedded along the circumference in a rotor thereof, and to an electric vehicle using such a permanent magnet type dynamoelectric machine.
A permanent magnet type dynamoelectric machine which is intended to reduce a cogging torque induced therein, JP-A-7-336808 (1995) discloses an arrangement for controlling and reducing cogging torque in such a permanent magnet type dynamo electric machine, by generating a torque for canceling out the cogging torque. Another measure for reducing such cogging torque is disclosed in JP-A-8-223832 (1996) in which a plurality of permanent magnets embedded in a laminated rotor iron core for the dynamoelectric machine are skewed with respect to the axial direction of the laminated rotor iron core.
Since, however, it is difficult to skew already shaped permanent magnets in the laminated rotor iron core, JP-A-8-223832 (1996) uses permanent magnets which are molded by injecting a resin containing powders of magnetic material while skewing the same, to reduce a cogging torque.
However, it is difficult to obtain molded resin type magnets having a uniform performance; and in addition, the cost of such magnets is high. Therefore, it is desirable to use already shaped magnets instead of such molded resin type magnets. In view of the difficulty of skewing the already shaped magnets as described above, it is desirable to devise a measure without skewing the same to reduce the cogging torque.